Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

SUMMARY
1According to ‘Gause's hypothesis’ a corollary of the process of evolution by natural selection is that in a community at equilibrium every species must occupy a different niche. Many botanists have found this idea improbable because they have ignored the processes of regeneration in plant communities.
2Most plant communities are longer-lived than their constituent individual plants. When an individual dies, it may or may not be replaced by an individual of the same species. It is this replacement stage which is all-important to the argument presented.
3Several mechanisms not involving regeneration also contribute to the maintenance of species-richness:


(a). differences in life-form coupled with the inability of larger plants to exhaust or cut off all resources, also the development of dependence-relationships,
(b) differences in phenology coupled with tolerance of suppression,
(c) fluctuations in the environment coupled with relatively small differences in competitive ability between many species,
(d) the ability of certain species-pairs to form stable mixtures because of a balance of intraspecific competition against interspecific competition,
(e) the production of substances more toxic to the producer-species than to the other species,
(f) differences in the primary limiting mineral nutrients or pore-sizes in the soil for neighbouring plants of different soecies, and
(g) differences in the competitive abilities of species dependent on their physiological age coupled with the uneven-age structure of many populations.


4The mechanisms listed above do not go far to explain the indefinite persistence in mixture of the many species in the most species-rich communities known.
5In contrast there seem to be almost limitless possibilities for differences between species in their requirements for regeneration, i.e. the replacement of the individual plants of one generation by those of the next. This idea is illustrated for tree species and it is emphasized that foresters were the first by a wide margin to appreciate its importance.
6The processes involved in the successful invasion of a gap by a given plant species and some characters of the gap that may be important are summarized in Table 2.
7The definition of a plant's niche requires recognition of four components:


(a) the habitat niche,
(b) the life-form niche,
(c) the phenological niche, and
(d) the regeneration niche.


8A brief account is given of the patterns of regeneration in different kinds of plant community to provide a background for studies of differentiation in the regeneration niche.
9All stages in the regeneration-cycle are potentially important and examples of differentiation between species are given for each of the following stages:


(a) Production of viable seed (including the sub-stages of flowering, pollination and seed-set),
(b) dispersal, in space and time,
(c) germination,
(d) establishment, and
(e) further development of the immature plant.


10In the concluding discussion emphasis is placed on the following themes:


(a) the kinds of work needed in future to prove or disprove that differentiation in the regeneration niche is the major explanation of the maintenance of species-richness in plant communities,
(b) the relation of the present thesis to published ideas on the origin of phenological spread,
(c) the relevance of the present thesis to the discussion on the presence of continua in vegetation,
(d) the co-incidence of the present thesis and the emerging ideas of evolutionists about differentiation of angiosperm taxa, and
(e) the importance of regeneration-studies for conservation.

The maintenance of species-richness in plant communities: the importance of the regeneration niche

The talk with present the key results of the IPCC Working Group III 5th assessment report. Concluding four years of intense scientific collaboration by hundreds of authors from around the world, the report responds to the request of the world's governments for a comprehensive, objective and policy neutral assessment of the current scientific knowledge on mitigating climate change. The report has been extensively reviewed by experts and governments to ensure quality and comprehensiveness.

Climate change 2014 - Mitigation of climate change

Seed dormancy is an innate seed property that defines the environmental conditions in which the seed is able to germinate. It is determined by genetics with a substantial environmental influence which is mediated, at least in part, by the plant hormones abscisic acid and gibberellins. Not only is the dormancy status influenced by the seed maturation environment, it is also continuously changing with time following shedding in a manner determined by the ambient environment. As dormancy is present throughout the higher plants in all major climatic regions, adaptation has resulted in divergent responses to the environment. Through this adaptation, germination is timed to avoid unfavourable weather for subsequent plant establishment and reproductive growth. In this review, we present an integrated view of the evolution, molecular genetics, physiology, biochemistry, ecology and modelling of seed dormancy mechanisms and their control of germination. We argue that adaptation has taken place on a theme rather than via fundamentally different paths and identify similarities underlying the extensive diversity in the dormancy response to the environment that controls germination.

/pdf/seed-dormancy-and-the-control-of-germination-4tdhm2985s.pdf

Seed dormancy and the control of germination

The proposal is made that seed scientists need an internationally acceptable hierarchical system of classification for seed dormancy. Further, we suggest that a modified version of the scheme of the Russian seed physiologist Marianna G. Nikolaeva be adopted. The modified system includes three hierarchical layers – class, level and type; thus, a class may contain levels and types, and a level may contain only types. The system includes five classes of dormancy: physiological dormancy (PD), morphological dormancy (MD), morphophysiological dormancy (MPD), physical dormancy (PY) and combinational dormancy (PY + PD). The most extensive classification schemes are for PD, which contains three levels and five types (in the non-deep level), and MPD, which contains eight levels but no types. PY is not subdivided at all but probably should be, for reasons given. Justifications are presented for not including mechanical dormancy or chemical dormancy in the modified scheme. PD (non-deep level) is the most common kind of dormancy, and occurs in gymnosperms (Coniferales, Gnetales) and in all major clades of angiosperms. Since, first, this is the class and level of dormancy in seeds of wild populations of Arabidopsis thaliana and, secondly, Type 1 (to which seeds of A. thaliana belong) is also common, and geographically and phylogenetically widespread, it seems that biochemical, molecular and genetic studies on seed dormancy in this model species might have rather broad application in explaining the basic mechanism(s) of physiological dormancy in seeds.

/pdf/a-classification-system-for-seed-dormancy-33n2carxeu.pdf

A classification system for seed dormancy

Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.

Seeds: Ecology, Biogeography, and, Evolution of Dormancy and Germination

Physical dormancy (PY) is caused by a water-impermeable seed or fruit coat. It is known, or highly suspected, to occur in nine orders and 15 families of angiosperms (sensuAngiosperm Phylogeny Group 1998), 13 of which are core eudicots. The Zingiberales is the only monocot order, and Cannaceae (Canna) the only monocot family, in which PY is known to occur. Six of the nine orders, and 12 of the 15 families, in which PY occurs are rosids. Furthermore, six of the families belong to the Malvales. The water-impermeable palisade layer(s) of cells are located in the seed coats of 13 of the families, and in the fruit coats of Anacardiaceae and Nelumbonaceae. In all 15 families, a specialized structure is associated with the water-impermeable layer(s). The breaking of PY involves disruption or dislodgment of these structures, which act as environmental ‘signal detectors’ for germination. Representatives of the nine angiosperm orders in which PY occurs had evolved by the late Cretaceous or early Tertiary (Paleogene). Anatomical evidence for PY in fruits of the extinct species Rhus rooseae (Anacardiaceae, middle Eocene) suggests that PY had evolved by 43Ma, and probably much earlier. We have constructed a conceptual model for the evolution of PY, and of PY+ physiological dormancy (PD), within Anacardiaceae. The model begins in pre-Eocene times with an ancestral species that has large, pachychalazal, non-dormant (ND), recalcitrant seeds. By the middle Eocene, a derived species with relatively small, partial pachychalazal, orthodox seeds and a water-impermeable endocarp (thus PY) had evolved, and by the Oligocene, PD had been added to the seed (true seed + endocarp) dormancy mechanism. It is suggested that climatic drying (Eocene), followed by climatic cooling (Eocene–Oligocene transition), were the primary selective agents in the development of PY. An evolutionary connection between PY and recalcitrance is suggested by the relatively high concentration of these two character states in the rosids. Phylogenetic data and fossil evidence seem to support the PY→(PY+PD) evolutionary sequence in Anacardiaceae, which also may have occured in Leguminosae.

Taxonomy, anatomy and evolution of physical dormancy in seeds

Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely-distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed-temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family. OUR FIRST STUDY of germination ecophysiology was undertaken as a project in Professor Elsie Quarterman's plant autecology class at Vanderbilt University in the spring of 1966. A literature search in connection with an investigation of the dormancy breaking and germination requirements of Aristida longespica and Sporobolus vaginiflorus (Baskin and Caudle, 1967) emphasized to us the need for studies on the germination ecology of mesic temperate herbs. Although many types of dormancy breaking requirements had been identified in seeds (Crocker, 1948; Crocker and Barton, 1957), this information had not been placed in context with germination phenology. Germination phenology had been described for a number of weed species (Bienchley and Warington, 1930; Chepil, 1946; Roberts, 1964), but not in respect to dormancy breaking and germination requirements of seeds. To determine how the timing of seed germination in herbaceous plants is controlled in nature, we combined descriptive studies of gerI Received for publication 26 January 1987, revision accepted 22 June 1987. From 1979 to 1985 part of our research was supported by grants from EPA (CR-806277-02) and USDA (82CRSR-21000) in connection with participation in the consortium for Integrated Pest Management (CIPM): Alfalfa Commodity. This support is gratefully acknowledged. This paper is dedicated to Dr. Elsie Quarterman, Professor Emeritus, Vanderbilt University, Nashville, TN. mination phenology with experimental studies of dormancy breaking and germination requirements. Numerous winter and summer annuals and monocarpic and polycarpic perennials were investigated, and these species were from various kinds of habitats including rock outcrops, fields, roadsides, pastures, mud flats, and deciduous forests. This is an ongoing effort; thus, while investigations of some species have been completed, other studies are in progress or being planned. To determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species, it has been necessary to study many species. GERMINATION PHENOLOGY -Freshly-matured seeds, collected mostly from plants in Kentucky and Tennessee, were used to study germination phenology in a nontemperaturecontrolled greenhouse-no heating or air conditioning and windows open all year in Lexington, Kentucky. Temperatures in this greenhouse were similar to those in the field (Baskin and Baskin, 1981a; 1985b). Continuous thermograph records have been kept since October 1969, when phenology studies were started. From 1969 through 1972, studies involved four replications of 200 seeds each sown on the soil

Germination ecophysiology of herbaceous plant species in a temperate region

The classic studies of Brenchley and Warington (1930) and numerous other investigations have demonstrated that large reserves (pools) of weed seeds accumulate in arable soils. Work reviewed by Kropad (1966) and Roberts (1981) shows that the number of seeds per m2 in the upper 15-25 cm of soil in cultivated fields may be as high as 70,000-90,000, and up to 95% of these may be contributed by annuals. Soil samples collected under vegetation of known age and history suggest that buried seeds of some weedy species may remain viable for 50100 years or more (e.g., Livingston and Allessio 1968, Oosting and Humphreys 1940). Seeds of 3 of 21 species buried in 1879 by W. J. Beal were viable after 100 years (Kivilaan and Bandurski 1981). In another experiment started by J. W. T. Duvel in 1902, buried seeds of 36 of 107 species were viable after 39 years (Toole and Brown 1946). Researchers have known for decades that many buried seeds need to be brought to the soil surface before they will germinate. To understand how germination of buried seeds is controlled, plant biologists have studied the re-

Carol C. Baskin

Papers

Seeds: Ecology, Biogeography, and, Evolution of Dormancy and Germination

A classification system for seed dormancy

Taxonomy, anatomy and evolution of physical dormancy in seeds

Germination ecophysiology of herbaceous plant species in a temperate region

The Annual Dormancy Cycle in Buried Weed Seeds: A Continuum